V. On the theory of the magneto-optic phenomena of iron, nickel, and cobalt

Abstract

1. In his ‘British Association Report’ (1893), on the “Action of Magnetism on Light,” Mr. Larmor points out that there are two possible ways in which the magnetic field may be regarded as affecting the phenomena of light propagation. “The imposed magnetisation is an independent kinetic system of a vortical character, which is linked on to the vibrational system which transmits the light waves,” and from the first point of view “ the kinetic reaction between the two systems will add on new terms to the electric force,” and so there would be a “ magneto-optic term ” in the expression for the kinetic energy. This type of theory includes Maxwell’s hypothesis of molecular vortices, and has been analytically treated by FitzGerald and Basset ; it also includes the theory developed by Drude in his paper “Magneto- optische Erscheinungen,” in ‘ Wiedemann’s Annalen,’ vol. 46. The great difficulty arises when one comes to consider the boundary conditions, as a discontinuity of electric force cannot be avoided; apparently the only satisfactory way of meeting this difficulty is to be found in Larmor’s suggested modification of FitzGerald’s analysis, involving the supposition that in the case of reflection of light at the surface of a magnetised metal the constraint introduces an irrotational or compressional wave of the ether set up at the reflecting surface and travelling with very great or infinite velocity through the space occupied by the metal; a satisfactory system of equations of propagation and boundary conditions is thus obtained by applying the principle of Least Action.